The present invention relates to concentrated herbicidal compositions comprising water soluble glyphosate salts and a surfactant.
A number of formulations have been proposed whereby the herbicide N-(phosphonomethyl)glycine, alias glyphosate, may be supplied as a concentrated aqueous solution with a surfactant synergist which aids wetting and penetration, when the composition is diluted and applied to herbage.
Factors governing the choice of surfactant include wetting power, herbicidal or synergistic action, environmental profile and ability to form stable solutions with glyphosate at as high a concentration as possible, as well as cost.
The surfactant which have so far proved most cost effective for these purposes have been ethoxylated amines. The latter however have a poor environmental profile being biotoxic and poorly biodegradable. There is a demand for a more environmentally acceptable alternative to amine ethoxylates.
We have discovered that ether carboxylates meet most of the above criteria but are insufficiently soluble in concentrated glyphosate solutions. We have furthers noted that amphoteric surfactants also meet most of the above criteria and can act as cosurfactants, solubilising ether carboxylates, but solutions of commercial amphoteric surfactants in concentrated glyphosate are unstable and have been found to deposit crystals of glyphosate salts.
Amphoteric surfactants comprise betaines, sulpho betaines and phosphobetaines. However the great majority of the amphoteric surfactants sold commercially are betaines. The betaines of commerce are normally made by quaternising an amine by reaction with sodium chloracetate. This reaction forms sodium chloride as an unavoidable by-product. As a result commercial betaines contain about 6 to 12% of sodium chloride. We have now discovered that it is possible to use amphoteric surfactants at the required levels in glyphosate solution concentrates without instability, if the sodium chloride content is substantially reduced. Low salt betaines typically contain less than 3% preferably less than 2%, more preferably less than 1% e.g. less than 0.5% especially less than 0.2% sodium ion expressed as wt. sodium chloride based on the weight of surfactant.
The invention provides a herbicidal aqueous solution comprising from 30% by weight, to saturation of a water soluble glyphosate salt and from 8 to 20% by weight of surfactant comprising 10 to 100% by weight based on the total weight of surfactant of an amphoteric surfactant and from 0 to 90% by weight based on the total weight of surfactant of ether carboxylate, said solution containing less the 0.035% by weight of sodium ion.
Sodium ion may be removed from amphoteric surfactants, either by electrosmosis, e.g. as described in our GB 1 525 692 or in EP 0 736 521, or by membrane filtration, for example as described in EP 0 626 881, or, less preferably, by displacing sodium ion with, for example, potassium or ammonium, e.g. using ion exchange. Alternatively, it is possible to prepare betaines with low salt levels by quarternising with acrylic acid.
The glyphosate is preferably present as its potassium, ammonium, C2 to 3 amine or mono or diethanolamine salt, or metho sulphate or as a mixture of two or more of said salts. Particularly preferred is the isopropylamine salt.
We prefer that the total level of inorganic salt be less than 0.39% by weight.
The amphoteric surfactant is preferably a betaine, e.g. a betaine of the formula: RR12N+CH2COOxe2x88x92, wherein R is an alkyl, alkenyl or alkyl phenyl group having an average of from 6 to 20, e.g. 8 to 14 aliphatic carbon atoms and R1 is an alkyl or hydroxy alkyl group having an average of from 1 to 4 carbon atoms. Particularly preferred are the so called quaternary imidazoline betaines, also called ampho acetates, and commonly ascribed the formula: 
(although they are actually present predominantly as the corresponding non cyclic amido amine) wherein R and Rxe2x80x2 are alkyl, alkenyl, cycloalkyl, alkaryl or hydroxyalkyl groups having an average of from 1 to 20 aliphatic carbon atoms and R preferably has an average of from 6 to 20, e.g. 8 to 14 aliphatic carbon atoms and Rxe2x80x2 preferably has 1 to 4 carbon atoms. Other amphoteric surfactants for use according to our invention include alkyl amine polyalkoxy sulphates, sulphobetaines and other quaternary amine or quaternised imidazoline sulphonic acids and their salts, and Zwitterionic surfactants, e.g. N-alkyl taurines, carboxylated amido amines such as RCONH(CH2)nN+Rxe2x80x22CH2COxe2x88x922 where n is 2 to 4, and amino acids having, in each case, hydrocarbon groups capable of conferring surfactant properties (e.g. alkyl, cycloalkyl alkenyl or alkaryl groups having from 6 to 20 aliphatic carbon atoms). Typical examples include 2-tallow alkyl, 1-tallow amido alkyl, 1-carboxymethyl imidazoline, 2-coconut alkyl N-carboxymethyl 2 (hydroxyalkyl) imidazoline, alkyl amido ethyl, propyl or butyl dimethyl betaine and C6-20 alkyl dimethyl betaine. Generally speaking any water soluble amphoteric or Zwitterionic surfactant compound which comprises a hydrophobic portion including C6-20 alkyl or alkenyl group and a hydrophilic portion containing an amine or quaternary ammonium group and a carboxylate, sulphate or sulphonic acid group may be used in our invention.
We particularly prefer short chain alkyl amido betaines, ampho acetates and alkyl betaines in which the alkyl group has 6 to 10 carbon atoms since they give very low foaming and permit high levels of ether carboxylate to be solubilised.
The surfactant preferably comprises at least 20% more preferably at least 30%, most preferably at least 40% e.g. 50 to 100% by weight of the amphoteric surfactant based on the total weight of surfactant.
We strongly prefer that the surfactant comprises an ether carboxylate. The ether carboxylate is preferably present in an amount of at least 10%, preferably more than 20% e.g. 30 to 60% by weight based on the total weight of surfactant. Generally the shorter the long alkyl chain of the betaines the higher the proportion of ether carboxylate that can be readily dissolved in a stable solution.
The ether carboxylate preferably has the formula R(OCH2CH2)nOCH2CO2xe2x88x92 wherein R is a straight or branched alkyl, alkenyl, alkylphenyl or polypropylene oxy group having from 6 to 20 e.g. 8 to 14 aliphatic carbon atoms and n is from 1 to 30, preferably, 2 to 20 e.g. 3 to 10.
The counter ion of the ether carboxylate may preferably comprise ammonium, potassium and or an amine or alkanolamine having up to six carbon atoms.
The surfactant may optionally but preferably comprise up to 20% by weight, e.g. 5 to 10% based on the total weight of surfactant, of a non-ionic wetting agent. The non-ionic wetting agent is preferably an ethoxylated alcohol such as a C6 to 25 straight or branched alkyl 1 to 30 mole ethoxylate e.g. a C10 to 18 alkyl 5 to 20 mole ethoxylate. The wetting agent gives better coverage of the leaf and superior herbicidal action.
We prefer that the surfactants should be pre-blended as a concentrate for supply to formulators of glyphosate compositions. To maintain sufficient mobility and to formulators of glyphosate compositions. To maintain sufficient mobility and dispersibility of such concentrates we prefer to add a suitable water miscible solvent such as a water miscible glycol or glycol ether, e.g. polyethylene glycol having a mean mol weight between 90 and 600 especially 130 to 250.
Such concentrates containing from 10 to 70% by weight ether carboxylate, from 20 to 80% by weight of low salt amphoteric surfactant and from 10 to 50% by weight of solvent are a further embodiment of the invention.
Preferably said concentrates additionally contain from 3 to 20% of a non-ionic wetting agent and/or from 1 to 6% of a sequestrant such as an aminophosphonate, e.g. of the formula.
(M2PO3CH2)2N[CH2CH2NCH2PO3M2]nCH2PO3M2
where n is from 0 to 10 preferably 2 to 6 and M is a compatible cation to provide a water soluble product.
The formulation may typically contain from 1 to 3% of sequestrant.
The concentrates contain, typically less than 70% water, preferably less than 60% water most preferably 10 to 55% water by weight of the concentrate.